B-DNA's dynamics and conformational substates revealed by calorimetric enthalpy relaxation and Fourier transform infrared spectroscopy

The combination of calorimetric enthalpy relaxation and its recovery with i sothermal FT-IR spectroscopic studies of the relaxing molecular motions is a powerful tool for investigating structure and dynamics of B-DNA. Hydrated fibers and films, with hydration level between 0.20 and 1.1 (g of water)/( g of DNA) were investigated. Isothermal relaxation of hydrated samples of t he sodium salt of DNA from salmon testes in the glass --> liquid transition region was compared with that of the hydrated nonoriented d(CGCGAATTCGCG)( 2) dodecamer. Between 180 and 220 K, relaxation toward equilibrium occurs v ia interconversion of the B-I to the Bn conformer substate of B-DNA. The ki netics of the effects on isothermal relaxation is described by a stretched exponential for both techniques. Relaxation times of polymeric B-DNA from s almon testes and of the dodecamer are, for a given hydration and temperatur e, nearly identical and therefore, the molecular motions involved must be l ocalized. (C) 2000 Elsevier Science B.V. All rights reserved.